Process for utilizing steam as a release agent in embossing



N 1963 M. o. BRUNSON ETAL 3,110,608

PROCESS FOR UTILIZING STEAM AS A RELEASE AGENT IN EMBOSSING Filed Dec. 12, 1960 Sheet Detector Sheet Fe ed Impression Heated Smooth Cup Spatula Knife Melt Grippers ll Idler R0 2 ldler Roll Pickup-Appliculor Roll (smoolh orgruvure I qEquqfizer Rod 0 (BOO-350F) slew ll Doctor Blclde l" I Chilled Roll 1 (highly polished,chrompluled Fountuln 45For less) (BOO-350%) 8: Rewind MARIO/V 0. BRU/VSO/V JAMES E. HUFFA/(ER INVENTORS ATTORNEYS United States Patent oTsSlNG .lames E. Huiialrer, Kin s astman Kodak (Io an of New Jersey 2, 19:?9, No. 75,4lill .s. (Cl. ELY/-16) Filed D This invention concerns a hot melt coating process and apparatus. More particularly, it concerns a high speed hot melt coating process employing the use of steam as elease agent in an embossing step and the apparatus arryin out this process.

employing hot melt coatings, it is often desirable to contact the coating against a chilled roll. This roll in case of certain types of polymeric coatings aids in crystallizing the coating. In other processes, the chilled roll is used to obtain a glossy uniform coating. In the event that the hot me t coating is used over printed illustions for stereoscopic effects, it may be desirable to nboss a lenticular design thereon.

When the hot melt is contacted against the chilled roll, there is often a strong tendency for the hot melt coating to adhere tenaciously to the chilled roll surface. Many attempts have been made to provide release agents on the chilled roll surface such as silicone oil, mineral oil, high boiling esters, various detergents and soaps, and the like. However, there has been a problem of sticking particularly when using an embossing cylinder, which results in jamming the machine and tearing the paper or other web substrate. If the equipment is run slow enough for these materials to provide satisfactory release, the surface or" the coating has often picked up undesirable properties due to the taking-up in the coating of some of the release agent. For instance, stress cracking and a general oily feel is common with the use of some of the agents such as silicone oil or mineral oil. Spraying or brushing of water on the chilled roll often resulted in a high concentration of water thus resulting in water marlrs on the finished product.

e requirements for coating colored pictures with a ho nelt coating to be subsequently embossed with a lenticular pattern involved critical characteristics in the hot melt coating such as transparency, foldability, resistance to abrasion and freedom from blocking. We have found that a blend of polyolefin materials with a iydrocarbon resin supplied these qualities. However, since these melts are cooled from approximately 370 F. to 48 F. in a split second, this blend tended to stick to the embossing roll after extended operation.

After extended investigation we have found that steam applied to the chilled roll in a certain manner effectively provides an almost molecularly thin film of water which s ves as a release agent rlOlli. resulting Water ma ks on the finished product.

One object of this invention is to provide an aqueous release agent for the chilled roll used in hot melt coatings. [nether object of this invention is to provide an appar tus for applying a hot melt coating to a paper or c in subs s employing a refrigerated embossing roll having steam ,cts directed thereon. A further object is to provide a method of coating an embossing roll with an almost molecularly thin film of water. An additional object is to provide a method of applying an aqueous layer to the embossing cylinder of a hot melt coating machine in controlled amounts by use of low pressure steam. Other objects will appear hereinafter.

in our preferred embodiment, we use a hot melt coating machine employing an embossing cylinder which operates at a temperature of 2060 F. This low tempera- Ii,llll,h08

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to ture is obtained by internal cooling of the cylinder using a source of chilled water or brine supplied thereto. A low pressure steam line is installed parallel to the embossing cylinder and containing small, as for example, holes drilled at /2 intervals. By the use of conventional steam traps and bypasses, all condensate may be eliminated. The steam line is maintained in such a way as to be adjustable at a distance from the embossing cylinder usually having the range of adjustment of from about 2 to 6 inches. By adjusting the steam line at a proper distance, steam escaping from the holes condenses uniformly on the cold embossing cylinder. As will be explained hereinafter the rate of steam flow is adjusted according to the rate of speed at which the machine is operating and removing the thin water film.

'i he accompanying drawings forming a part of this application illustrate embodiments of our apparatus.

FIGURE 1 is a diagrammatic representation of our apparatus employed in applying a hot melt coating on colored pictures intended to have a stereoscopic effect due in part to the lenticular coating elfect obtained by employing a certain type embossing rol 2 is a diagrammatic representation of a single roll kiss coater with an equalizer rod.

in FEGURE l the colored picture in the form of sheets of paper is fed between the coating roll 1 and impression roll 3 where the hot melt 7 applied by the heated spatula knife to the roll 1 was transferred to the paper substrate. The picture on the paper substrate passes between impression roll 3 and refrigerated embossing roll 2 around to talze-oii' reel and take-off reel 5. Steam is applied through perforated steam pipe 6.

in FIGURE 2 the paper substrate passes around the idler roll 13 to coating roll 1. This coating roll picks up rot melt coating 8 which coating is rendered uniform on the coating roll it by the doctor blade ll. The coated paper passes equalizer rod it? which smooths the coating, then past idler roll 12, and around chilled roll 2. Steam is applied through perforated steam pipe 6 to the chilled roll 2. The coating thickness may be controlled by the tension on the web being coated, adjustment of the doctor blade ll, and the temperature of the melt 3.

Although in many emobdiments, we have found 10 l s./sq. in. steam may be used, the exact steam pressure is not a limit; ion on the present invention. Ho ever, the steam should be dry having the condensate removed therefrom. The desirable steam pressure is determined by the distance between the steam line and the cooling (embossing) cylinder, the size of the cooling cylinder, and the speed of the machine. Since the release properties are obtained by condensing the steam on the cold embossing cylinder, the primary requirement for steam pressure is that it be sufficient to provide the necessary velocity to reach the embossing cylinder at a uniform rate and in adequate quantities. The cooating thickness in our preferred embodiment is 10 mils, but it may by varied from 1 mil to 15 mils. The size of the steam lines, the diameter of the holes in the steam lines, and the distance between the holes may be varied to provide adequate coverage of the steam against the surface of the chilled roll.

The following examples illustrate preferred embodiments of our invention.

Example I then set into operation until sheets had been coated with a coating thickness of 6 mils. After the first three sheets had been coated, no visible signs of Water marking had occurred. There was a noticeable increase in the gloss of the coating after the third sheet. A ing of these coated sheets showed no damaging effect as a result of the steam used as a release agent. The sheets released readily in continuous high speed operation of the machine.

Example II The coating process described in Example I was repeated except that a mil coating was applied to 50 sheets. Excellent results were obtained. On previous attempts to coat a 10 mil film without using the present invention, it was necessary to spray the embossing cylinder after every fifth sheet with a release oil. This often resulted in discarding the sixth sheet since it was heavily coated with the oily release agent.

Further details concerning the preferred coating compositions employed in the above examples are described in our companion copending application Serial No. 76,147 entitled Hot Melt Composition For Three-Dimensional Printing in the names of Brunson and Hutfaker, filed December 16, 1960.

Other hot melt compositions may be used in the apparatus described in FIGURES 1 and 2 using steam as the release agent. These hot melt coatings include various Wax formulations, cellulose esters, polyolefins, polymeric Waxes, and the like.

It will also be apparent that although this method'of treating the chilled roll is particularly adaptable for hot melt coatings, it can also be used for contacting against the chilled roll when the coating has been extruded on the substrate. In addition to being used for coating various kinds of colored pictures on a paper base, the present invention may be used to coat webs carrying printing or other markings.

The thin film of Water, which results from the application of steam in accordance with the resent invention, has a thickness of 1 to 10 microns to give good results in our invention.

Our invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be elfected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A process for hot-melt coating which-comprises coating a polymeric hot melt composition onto a substrate, bringing the hot coating into contact with an embossing roll the surface of which is at a temperature of about 2060 F. and contacting the embossing roll prior to contact with the coating, with steam suflicient that a film of liquid water of a thickness of about 1 to 10 microns is condensed thereon, and removing the resulting chilled embossed coating on the substrate from the surface of t e embossing roll.

2. A process for obtaining release of an embossed polymeric coating from an embossing roll, which comprises bringing the coating into contact with an embossing roll the surface of which is at a temperature of about 20-60 F. and contacting the embossing roll prior to contact with the coating, with steam sufiicient that a film of liquid water of a thickness of about 1 to 10 microns is condensed thereon, and removing the resulting chilled embossed coating from the surface of the embossing roll.

3. A process of providing a lenticular pattern on the surface of a polymeric hot-melt coating which comprises bringing the coating while in a softened condition into contact with a lenticular embossing roll the surface of which is at a temperature of about 20-60 F. and contacting the embossing roll prior to contact with the coating, with steam suflicient that a film of liquid water of a thickness of about 1 to 10 microns is condensed thereon, and removing the resulting chilled coating having a lenticular pattern on its surface from the embossing roll.

4. A process providing a lenticular pattern on the surface of a picture which comprises applying a polymeric hot-melt coating to the surface of the picture, bringing the coating into contact with a lenticular embossing roll the surface of which is at a temperature of about 20-60" F. and contacting the embossing roll prior to contact with the coating, with steam sufficient that a film of liquid water of a thickness of about 1 to 10 microns is condensed thereon, and removing the resulting lenticular embossed picture from the surface of the embossing roll.

References Cited in the file of this patent UNITED STATES PATENTS 2,598,264 Jones et al. May 27, 1952 2,829,980 Redd Apr. 8, 1958 2,950,989 Freeman Aug. 30, 1960 

1. A PROCESS FOR HOT-MELT COATING WHICH COMRISES COATING A POLYMERIC HOT MELT COMPOSITION ONTO A SUBSTRATE, BRINGING THE HOT COATING INTO CONTACT WITH AN EMBOSSING ROLL THE SURFACE OF WHICH IS AT A TEMPERATURE OF ABOUT 20-60*F. AND CONTACTING THE EMBOSSING ROLL KPRIOR TO CONTACT WITH THE COATING, WITH STEAM SUFFICIENT THAT A FILM OF LIQUID WATER OF A THICKNESS OF ABOUT 1 TO 10 MICRONS IS CONDENSED THEREON, AND REMOVING THE RESULTING CHILLED EMBOSSED COATING ON THE SUBSTRATE FROM THE SURFACE OF THE EMBOSSING ROLL. 